A user authentication method with enhanced security is provided. The method includes generating a first common authentication key if a user of the user terminal enters a private password and providing the generated first common authentication key to an authentication server, registering the first common authentication key and user information by matching the first common authentication key with the user information, generating a second common authentication key in real time if the user enters the private password, generating a server authentication key, generating first server authentication information by calculating a one time password (OTP) by using the server authentication key as an operation key, generating a user authentication key, generating first user authentication information by calculating an OTP by using the user authentication key as an operation key, and performing user authentication based on whether the first server authentication is identical to the first user authentication.